Paper board, including corrugated paper board, is commonly used to provide insulation for various products, including paper cups. Traditionally, corrugated paper board is prepared by first forming a corrugated element, or “medium”, by passing a cellulosic sheet between corrugating rolls forming a substantially sinusoidal or serpentine cross-section in the sheet. The tips of the sinusoidal portion are referred to as flutes. An adhesive is commonly applied to the tips of the flutes, and a noncorrugated or planar cellulosic liner is applied against the adhesive coated flutes of the corrugated elements as the corrugated sheet passes between a corrugating roll and a pressure roll. A resulting paper product having the corrugating medium on one side and the planar liner on another side is called a single-faced web. The single-faced element may be used as is in certain applications as a liner or buffer material within a container. In some products, the adhesive is also applied to the flute tips of the single-faced web and a second liner sheet is subsequently applied to the fluted medium in a “double faced” operation. The second liner sheet is exposed to conditions of heat and pressure during its contact with the adhesive. In practice, the sheet of corrugated cardboard most frequently encountered has two plane sides placed on each side of the corrugated medium. Depending on the specific strength desired, a sheet of corrugated board may also be provided with a more complex structure, such as two corrugated mediums and three plane surfaces, two outer ones and one inner one separating the two corrugated medium.
Starch-based adhesives are most commonly used in the corrugating process due to their desirable adhesive properties, low cost and ease of preparation. The most fundamental starch corrugating adhesive, commonly referred to as a “Stein-Hall” formulation, is an alkaline adhesive that is comprised of raw, ungelatinized starch suspended in an aqueous dispersion of cooked starch. The adhesive is produced by gelatinizing starch in water with sodium hydroxide (caustic soda) to yield a primary mix of gelatinized or cooked carrier, which is then slowly added to a secondary mix of raw (ungelatinized) starch, borax and water to produce the fully formulated adhesive. In conventional corrugating processes, the adhesive is applied to the tips of the fluted paper medium or single-faced board, whereupon the application of heat and pressure causes the raw starch to gelatinize, resulting in an instantaneous increase in viscosity and formation of the adhesive bond.
While typical adhesives are sufficient to adhere the various layers of the insulating paper together, these adhesives do not act as insulation themselves. Thus, in typical situations, there is required at least two layers of paper (the liner and the medium), and in many situations three layers are required (two liners and the medium). To achieve proper insulation, typical insulating products require the medium to have a fairly high amplitude in its wave pattern, requiring more paper to be used in formation of the medium. These typical formulations result in a tremendous amount of paper to be used for the product, which not only adds cost to the production but also is not environmentally sound.
The present invention seeks to improve insulating papers, through the use of an adhesive composition that adds insulative properties to the product. In addition, the adhesive and the products made therefrom are made from natural components and are environmentally conscious. The present invention provides an environmentally sound insulating adhesive that provides sufficient adhesion to the product upon which it is being applied.